CNN/Gallup Poll; Poll Junkies reply

The latest CNN/Gallup poll has such disparate numbers compared to the Time poll.  Bush's approval at 60%.  Bush creams Dean while in the Time poll it is within the margin of error.

Could someone who is very poll savvy tell me why the CNN/Gallup Poll is always uniformly more favorable to Republicans than other polls like the last Time magazine poll.

Do they have a model which has more Republicans in than other poll.  The questions seems to be the same. Do they call people differently?

This bias was true in 2000.  Anyone got ideas.